The present invention relates to a decorative component for a vehicle that decorates the vehicle and has transmittance of millimeter waves from a millimeter wave radar device.
A vehicle may have a millimeter wave radar device on the rear side of a decorative component for a vehicle, such as a front grille or an emblem, to measure the inter-vehicle distance or the distance from an obstacle using millimeter waves. Conventionally, the millimeter wave radar device temporarily stops measurement when snow adheres to the decorative component. However, as use of a millimeter wave radar device becomes common, it is demanded that measurement be continued regardless of snow.
To meet the demand, a snow melting function may be added to the decorative component. For example, a decorative component for a vehicle disclosed in Japanese Laid-Open Patent Publication No. 2004-138572 includes a decorative body portion configuring a main portion of the decorative component and a heater wire arranged on the front surface of the decorative body portion. The heater wire has a plurality of parallel linear sections spaced apart at regular intervals. Also, a groove portion is arranged between each adjacent pair of the linear sections of the heater wire on the front surface of the decorative body portion. The groove portions extend parallel to the linear sections. In this decorative component for a vehicle, the snow adhering to the front surface is melted and converted into water by the heat generated by the heater wire. The water then flows down in the groove portions and is drained from the decorative component.
A decorative component for a vehicle disclosed in Japanese Laid-Open Patent Publication No. 2002-22821 includes a decorative body portion configuring a main portion of the decorative component and a metal layer arranged on the decorative body portion. The decorative component electrifies and heats the metal layer, thus melting the snow adhering to the decorative component.
There is a demand that a decorative component for a vehicle should decrease attenuation of millimeter waves when the millimeter waves are transmitted through the decorative component. On the other hand, it has been discovered that there is a constant relationship between the attenuation amount of millimeter waves and the thickness of a decorative component for a vehicle. More specifically, it has been discovered that the attenuation amount of millimeter waves is small if a decorative component for a vehicle has multiple thicknesses that satisfy a certain condition. However, in the decorative component for a vehicle disclosed in Japanese Laid-Open Patent Publication No. 2004-138572, the groove portions in the front surface of the decorative body portion form an uneven surface of the decorative body portion. This makes it difficult to decrease the attenuation amount of millimeter waves.
In the decorative component for a vehicle disclosed in Japanese Laid-Open Patent Publication No. 2002-22821, the millimeter waves transmitted from a millimeter wave radar device may be reflected by the metal layer.
Although the heater wire described in Japanese Laid-Open Patent Publication No. 2004-138572 and the metal layer described in Japanese Laid-Open Patent Publication No. 2002-22821 each exert a function of melting adhering snow, the heater wire and the metal layer interfere with millimeter waves when the millimeter waves are transmitted through the respective decorative components and thus may decrease the transmittance performance.
Therefore, even though Japanese Laid-Open Patent Publications No. 2004-138572 and No. 2002-22821 are capable of melting adhering snow, both can be further improved to ensure proper transmittance of millimeter waves.